Navigation light changer having lamp current monitor



Allg- 1961 H. R. SMYTH 2,998,545

NAVIGATION LIGHT CHANGER HAVING LAMP CURRENT MONITOR Filed May 26, 19582 Sheets-Sheet 1 R3 R4 TR2 34 :l I3 R18 TRA TRB TRC TRD TRE RI? 22 23RIG 22 l l l I Potential on i .TRD collectors of m ME 4/ I T|ME T 1 2INVENTOR I 7 HENRY LYALL R055 SMYTH l 1 lumen output I i 1 1 P1 0651- A;9 Z 2 l I AGENT Aug. 29, 1961 Filed May 26, 1958 H. L. R. SMYTH2,998,545

NAVIGATION LIGHT CHANGER HAVING LAMP CURRENT MONITOR 2 Sheets-Sheet 2 I!al "Will M In lllifi 1 INVENTOR HENRY LYALL R055 SMYTH AGENT UnitedStates Patentf'O 2,998,545 NAVIGATION LIGHT CHANGER HAV'IN LAMP CURRENTMONITOR Henry Lyall Ross Smyth, Ottawa, Ontario, Canada, as-

signor to National Research Council, Ottawa, Ontario, Canada, acorporation of Canada Filed May 26, 1958, Ser. No. 737,769 4 Claims.(Cl. 315-89) earlier application Serial 664,605, filed June 10, 1957, I

for Automatic Lamp Changers, now Patent 2,892,966.

Navigational marker lights installed on buoys, particularly unattendedbuoy lights situated in remote locations serving inland waterway andcoastal marine craft, are required to operate reliably for long periodsof time without attention. Such lights desirably are fitted withautomatic lamp replacement apparatus to provide continuity of service,and in some installations lamps are deliberately energized above theirrated voltage in increase efiiicency, necessitating more frequentreplacement. The number of inspections per year or per season which ithas heretofore been found necessary to carry out in order to maintain agiven standard of performance of the complete installation has incurreda costly upkeep charge. The maintenance problem is particularlyaggravated when the marker lights are located in hazardous waters and atvery distant sites.

The apparatus presently in use is characterized by complexity and bulk,involving motor-actuated switch devices and circuit breakers forinterruptedly energizing a stepping motor magnet in response to an openlamp circuit condition. These devices have required frequent attentionto the switching contacts.

Heretofore apparatus devised for and employed at unattended navigationmarker lights for detecting a lamp failure has depended on change in theresistance of a lamp filament circuit, for example the change from usualopcrating resistance to substantially infinite resistance of a broken orburnt out filament. A defective lamp disables a detecting relay, whosecontacts remain closed, thereby supplying battery to an electromagneticstepping motor which is self-interrupting by means of a mechanicallinkage to the detecting relay, and drives a turret loaded with lampsconnected to switching segments until a good lamp is in circuit. Thedetecting relay and the self interrupting stepping relay have bothproved to be sources of trouble, the interrupter contacts in particularbeing susceptible to sticking or failure, due to maladjustment.

Accordingly this invention is concerned to provide th combination of aperiodic switching circuit which does not use moving contacts employingtransistor devices for energizing a signal lamp at intervals, withmotor-driven lamp-changing mechanism energizable under control of amonitor circuit responsive to lamp flashing to inhibit functioning ofthe mechanism unless the lamp fails to light in an energizing interval.

It is a further object to provide a simplified control for lamp changingmechanism wherein a transistor switching stage periodically energizes asolenoid winding whose armature is coupled with pawl and ratchet drivemeans to advance the mechanism in response to failure of a lamp to lightwith suflicient brightness.

Yet another object is the provision of low cost and efiicient monitormeans for detecting the magnitude of a filament current in a flashinglamp and for controlling energization of simple and reliable solenoidpowered paWl-and-ratchet driven lamp changing mechanism during the flashinterval in response to detection of a current less than a predeterminedmagnitude.

Other objects and features will become apparent in a careful reading ofthe following description of the invention and of practical means ofcarrying it into effect and by study of the accompanying drawings, inwhich,

FIGURE 1 is a schematic circuit diagram of a lamp flasher with lampcurrent monitor and changing mechanism operative according to theinvention;

FIGURES 2 and 3 are graphs relating keying waveform, lumen output, andmonitor responses of the apparatus of FIGURE 1;

FIGURE 4 is an elevation view, partly in cross-section, of a completeflashing light assembly showing a lam turret, Fresnel lens and controldevices;

FIGURE 5 is an alternative corrective circuit for the monitor amplifier;and

FIGURE 6 is an enlarged cut-away elevation view of the mechanical drivefor a lamp turret of FIGURE 1.

An economical and relatively low cost flasher system havingdaylight-responsive inhibiting means'to discontinue flashing whenambient light rises above a predetermined level is described and claimedin applicants copending application entitled Lamp Flasher WithDaylight-Responsive Inhibiting Means, Unites States Serial No. 657,365,filed May 6, 1957, now Patent No. 2,891,195. The operation of thecircuits and devices of an embodiment described in the relatedapplication, which is incorporated in FIGURE 1 of this application, isincluded here to assist in more fully comprehending the presentinvention. Briefly, a pair of transistors TR1 and TR2 preferably PNPjunction type have their collectors and bases cross-connected byrelatively large capacitance means C1 and C2; each base is shunted toits respective collector by individual shunt resistors, R3 and R4, .withindividual resistors R2 and R5 in series with the collectors wherebywith emitters positively polarized by a source of supply, as by bus 60connected with supply positive lead 13, a multivibrator operation isachieved with one transistor switched to fully on state while the otheris biassed o for a predetermined duration, and thereafter a reversal ofstates ensuing. The circuit is freely running as long as operatingvoltages are applied. By arranging that capacitor C2 is the smaller, theon time for TR2 is made to be a fraction of the recurrence period, thevalue of shunt resistor R4 being adjustable to control the flashes perminute switching rate.

The keying waveform appearing on the collector of TRZ may be examined byreference to FIGURE 2, wherein substantially full supply voltagepotential appears as TR2 is duly biassed on during the interval F, andsubstantially negative supply potentil appears during the remainder ofthe recurrence period T. During the interval F no current flows in thelow-valued coupling resistor R7 out of the base of relaying stagetransistor TR3, hence this stage is switched off. There is thereforesubstantially negative supply potential at the collector end of thecoupling resistor R9 which is also of low value hence stage TR4 isstrongly biassed on. erably a relatively high current type of transistorwhose emitter passes the total of all thebase currents of the switchingstage comprising TRS, TR6 connected in parallel.

A group of lamps which may be four or any other convenient number, ofwhich but the lamps 12 and 12 are The latter is prefindicated in FIG. 1,have one terminal of their filaments connected to a common ground bus onthe turret axle, and their individual other filament terminals connectedto corresponding commutator segments spaced at equal angular intervalsabout the axis of rotation of the turret, only segments 16 and 16 beingindicated in the drawing.

In the position shown for the lamp turret a fixed wiper 15 completes theflashing circuit through lamps 12 by way of the emitter-collector pathsof the switching stage, including the small test resistor R8 in seriestherewith, from the positive supply bus 13. Accordingly, as the keyingstage is switched on during a fish interval F, as is graphicallyillustrated in FIG. 2, the lamp filament lights, and thereafter remainsdark throughout the remainder of the recurrence period T.

During flash interval F, positive potential is applied from thecollector bus 25 of the switching stage to a lead 29 which providespositive supply to the monitor amplifier group of transistors, TRA, TRB,TRC, TRD, and TRE. It will be observed that the potential of the lowerend of resistor R8 will always be the potential of the bus 25 common tothe collector electrodes of TRS and TR6. An additional conductor 58 ispermanently connected to the upper end of resistor R8 and with the baseof the transistor TRA of the monitor amplifier. Resistance R8 is chosento be of such value that at the desired operating current through lamp12, the voltage drop between its terminals is a small fraction of avolt; for example, when lamp 12 draws a current of 0.46 ampere from anominal 6-volt supply, resistor R8 in one specific embodiment had apotential between its ends of 0.15 volt during a flash interval.

With an operative lamp properly positioned in circuit, and appropriateoperating voltages applied to conductors 13, 14, the potential ofconductor 58 during the flash interval will fall by a fraction of 21volt below that of the emitter of TRA, whereby the emitter-to-collectorpath of this transistor is caused to be conducting. Accordingly, thestate of the individual transistors TRA to TRD inclusive is determinedby the direct resistance coupling between the collector of a precedingstage with the base of the following stage, whereby TRA and TRC arebiassed "On while TRB and TRD are biassed Off. The potential of the baseof TRE is substantially that of its emitter, due to zero voltage dropacross R16, whereby base current is substantially zero and TRE isbiassed fully Oir. It will therefore be apparent that no current canflow in the winding of lamp changer solenoid 20 through the final stageTRE of the monitor amplifier so that the turret remains unmoved. At theend of each flash period the potential of conductor 29 fallsubstantially to zero as TRS and TR6 are biassed 01?, so that duringrest periods the entire monitor amplifier is disabled.

Should lamp 12 fail, as for instance in the event of disintegration ofthe filament for any reason, or if the resistance of the entire lampcircuit including contact resistances, should rise appreciably, thevoltage drop across test resistor R8 during a flash interval will beless than a predetermined amount, or even zero. If the bias applied tothe base of TRA under such conditions fails to make TRA sufi'icientlyconducting to cause TRB to be biassed off, armature 21 of electromagnet20 will be pulled down due to current flow therein via theemitter-collector path of TRE, against the force of restoring spring 30.As a result ratchet wheel 23 is thereby caused to move under action ofpawl 22 by one tooth distance. At the termination of the intervalarmature 21 is restored to its rest position, and the pawl is retractedready to re-engage the ratchet as described, when the potential ofconductor 29 falls to zero.

Referring to FIG. 6, it will be seen that turret body 32 is coupled topinion 24 on the shaft of ratchet 23 for mechanical drive thereby sothat in each succeeding interval as TRS and TR6 are switched On, thegroup of lamps is advanced by an increment of angular displacement,eventually bringing another segment and lamp into the circuit, as forexample segment 16 and lamp 12. With the restoration of flashing bysubstitution of a new andoperative lamp as load for the switching stageTRS and TR6, the output of stage. TRB of the monitor amplifier is againinhibited and electromagnet 20 ceases to be energized so long as lamp12' remains operative.

While the interposition of any resistance load in series between aconstant voltage supply such as a battery and the filament of a lamp isgenerally to be avoided in the interests of efliciency, it is entirelysatisfactory in the embodiments of the present invention since testresistance R8 may be made so small as to leave substantially full supplyvoltage to be applied across the lamp itself. In general apart fromconsiderations of cost of battery supply and of the monitor system, thewattage load of the monitor amplifier group of transistors, the flashbrilliance of a lamp in the circuit, and the ratio of useful lamp wattsto all other dissipative loads, will be proportioned to satisfy therequirements of a given installation. The test resistance R8 may be madeto be less than one percent of the filament resistance of an energizedlamp, with appropriately high gain being provided in the monitoramplifier stage. In one actual circuit foundto be suitable, R8 had avoltage drop across its terminals during the flash interval of 0.15 voltwhile 6.10 volts drop was measured across the lamp filament, whenoperated from a nominal 6 volt supply battery having open circuitvoltage, fresh, of 6.8 volts. The loss of intensity of light output ofthe lamp due to test resistor R8 as compared with output at the samesupply voltage without R8 was observed to be slight. In thisinstallation, during a flash interval, the ratio between wattsdissipated in the lamp load and the watts taken by all other dissipativeloads including TRA and TRC and the resistor R8, was as 2.93 watts to 91milliwatts, indicating an efliciency of approximately 97%. Theimprovement over the prior art represented by this figure may beappreciated by considering that in the monitor circuits heretoforedevised employing series or shunt electromagnetic relay detectorsassociated with a lamp circuit the efficiency figure has been of theorder of The monitoring function described above may be realized atrelatively low cost, and the resistor R8 may take any suitable form. Apreferred form comprises a short length of resistance wire such asAdvance, #18 B. & S. gauge, having 0.182 ohm per foot.

The reliability of a monitor device according to the invention has beenfound to be superior to any prior art device known to applicant,attributable for the most part to absence of moving contacts in thesystem, and providing that only the turret segments and axle arefriction contacts, which operate at extremely low duty cycles.

A characteristic of filamentary incandescent lamps is that the waveformof lumen output with time (FIG. 3) does not coincide with the keyingwaveform (FIG. 2) due to the finite time or delay interval AF requiredfor the filament to heat up to a light-emitting temperature. The delayinterval is reducible by choice of a lamp with a filament of relativelysmall mass, but cannot be made zero. However the energization ofelectromagnet 20 will inherently be prevented as soon as the lampcurrent begins to flow, coincident with the application of the positivevoltage keying wave to the stages TRA, TRB, TRC, TRD, and TRE. Tosafeguard the system against any possibility of an initial current spikeflowing in winding 20, the wave may be deliberately delayed by aninterval of at least the length AF.

A circuit for delaying application of positive potential to the monitoramplifier is shown in Figure 5 wherein stage TRD is shown having a delaycapacitor C4 connected from the positive bus to the base. Chargingcurrent through the capacitor flowing inresistors R19 and R15 tonegative supply effectively biasses the stage off until the capacitorhas reached a degree of charge.

A practical embodiment of the invention is described with reference toFIGURES 4 and 6. A lamp turret 32 having a capacity of four lamps hasits axle journalled in a frame comprising the upward extension of acasting 33 having a gear train housing closed by cover plate 55 and aback bearing plate 36-. The lamp turret assembly is supported with theframe base 37 secured to a thick disc cap 40, as by screws or othersuitable fastening means, thereby securing a strap 38 to the assembly.Stud bolt means 39 passed through the ends of the strap are threadedlyengaged in holes tapped into the main lamp base 10. A Fresnel type lens11 is carried upon a sturdy metal base ring 50 having a series ofcaptive bolts 51 spaced about the circumference, the base seating onbevelled face 49 of the lower housing. Suitable resilient sealing gasketmeans are provided to prevent dust and moisture from gaining entry whenthe bolts 51 are tightened down upon the slotted ears 52. Forconvenience the upper lens assembly is made to pivot upon the lowerhousing, hinging on pin 56 which is received in the hole 57 of the baseshoulder provided.

Base may be supported in any suitable manner upon a buoy, tower, mast orother vertically extended structure, negative supply lead 14 from thebattery being grounded to frame and positive lead 13 into the borepreferably through a sealing gland received in the side of the base.

A daylight-sensing photocell 34 is housed on the side of the back geartrain plate 55 and is preferably shielded from direct lamp illuminationas by a blackened sheet metal rectangular structure 35 built around it.The cell receives ambient illumination incident upon it as istransmitted inwards through the lens 11. When the resistance of the celldecreases sufiiciently as a result of ambient illumination, currentflows from the positive supply lead 13 (see FIG. 1) through the Windingof relay M, drawing armature 59 away from contact 58 and therebydeenergizing the buss 60. It will be seen that whenever the intensity ofambient light on cell 34 remains low, buss 60 remains at positivepotential to energize motor supply buss 29 and lamp supply wiper 15 inparallel via switching transistors TR5, TR6. The disabling relay M issupported on the amplifier chassis 43 which depends from the lid 40 andis hermetically enclosed in the cup 41, shown in cut-away section.O-rin'g seals are provided between the upper flaring part of can 41 andthe bevelled face of lid 40, between which parts pressure is maintainedwhen assembled, by suitable bolt means (not shown). Light flash monitorcell 17 which may be employed as an alternative control to the input ofTRA as in applicants Patent 2,892,966, supported adjacent the base ofthe operating lamp, indicated in FIGURE 6 as lamp 12, is preferably setat an angle of 45 degrees with the vertical and facing upwardly towardsthe filament, so

as not to obstruct light which is radiated substantially uniformlythrough the equatorial plane of the lens. A sheet metal tab supportingstructure 28 is suitably affixed upon the upper part of the casting 33.The series of lamps are detachably supported in any convenient mannerupon the turret block 32, the support herein being indicated as pairs ofscrew heads 54, under which the lamp sockets are received and againstwhich they are pressed outwardly by spring tension of the base contact.

Lamp energizing circuit leads are taken from the switching circuit byway of binding posts 47, 48, the latter being grounded to the frame andthe former being insulated and connected to suitable wiper means 15 (notshown) for contacting segments located on the turret on which the lampfilament leads terminate.

A solenoid stepping motor of conventional type is shown in FIGURE 6,operating ratchet wheel 23 by means of a pawl spring 22, wherein theturret 32 is driven by means of the gear train comprising gear 46,pinion 45,

gear 44-, and pinion 24. At each energization of wthe sole{ noid 20, thearmature 21 pulls down and advances pawl 23 by one tooth distance. Alesser or a greater number of gears and other gear ratios may be useddepending on the particular application in which the lamp is used. Inthe present instance, where the flashing rate is approxi mately 12flashes per minute, a new lamp may be restored into the circuit in lessthan half a minute.

The invention extends also to motor means other than thesolenoid-actuated pawl-and-ratchet stepping motor shown. The latter ispreferred as completely avoiding any moving contacts, but it is to beunderstood as entirely an equivalent to employ a brush type D.C. poweredrotary electric motor, whose shaft is linked in driving relation toturret 32 by means of a suitable gear train.

Where the number of lamps carried by the turret is small, a spring motorof only such capacity as would suffice to rotate the turret only a fewrevolutions and powered adequately for at least one revolution may beemployed, in conjunction with a solenoid actuated brake, stop, or dog torelease the stop when a new lamp is to be substitued. Such spring motorsand controls are believed to be well understood and suitable devices fordriving a turret may take many forms.

The invention extends moreover to devices wherein the lamp energizationis intermittent but the length of a flash may be several hours or evendays, provided that the means controlling the motor operation is itselfpowered in common with the lamp energizing circuit, so that the motor isineffective to drive the lamp changer mechanism except in periods whenthe lamp is supplied with energizing current.

While the invention has been particularly described with reference to asmall type of lamp used in navigational marker lights, it is applicableto a wide range of installations and extends to all signal andilluminating devices as are required to operate reliably in steady orflashing lightt generating service, on fixed installations or invehicles such as automobiles, boats and aircraft.

I claim:

1. In a signal device having a drive mechanism for a lamp carrier toposition lamps and lamp circuit terminals for connecting a positionedlamp with an intermittent supply of electric current, the improvementcomprising a lamp current test resistor connected in series with saidcircuit producing a test voltage across the resistor proportional tolamp current, said resistor having a resistance value of from about 0.01to about 0.08 times the resistance of said lamp circuit when a lamp is.operating an electromagnetic driving motor for operating said mechanismand having a winding, and a drive control for said driving motorconnecting said supply to said winding, said control comprising theemitter-to-collector path of a transistor having a base electrodedetermining the conduction state of said path, a direct-coupled voltageamplifier fed from said supply and having an input and delivering itsoutput to said base electrode, and means appliying said test voltage tosaid amplifier input whereby to block said emitter-to-collector pathwhen said test voltage exceeds a predetermined value and to energizesaid motor winding by current through said path when said test voltageis less than said value.

2. The device of claim 1 wherein said test resistor is permanentlyconnected between said supply and a terminal of said lamp circuit andsaid terminal is separably connected with the filament of a positionedlamp moved by said carrier, and said amplifier comprises a plurality ofresistance coupled transistor stages in cascade having said terminalconnected permanently with the base electrode of the first stage to biassaid base according to the potential difference across said resistor,and wherein each stage is fed from said supply in parallel with saidemittear-collector path.

3. The device of claim 2 wherein said driving motor means and said drivemechanism comprise a solenoid having an armature, a pawl carried by thearmature, a

ratchet wheel engaged by said pawl, and coupled with said lamp carrierto effect a predetermined movement of said carrier upon energizationfrom said supply, said movement being a fraction of the totalvcarriermovement required to replace a subsequent lamp in operating position.

4. In a signal device of the type comprising a carrier for a pluralityof lamps moveable to position lamps sucoessively in operating positionand including contact means for connecting a positioned lamp in serieswith a lamp energizing circuit, a solenoid drive motor for advancingsaid carrier, and an intermittent source of electric current forsupplying said circuit and said solenoid to cause said lamp to lightduring a flashing period and to tend to move said carrier concurrentlywith said flash, the improvement which comprises control meansresponsive to failure of a positioned lamp efiective to cause said motorto advance said carrier until a correctly functioning lamp is inposition and thereafter to hold said carrier stationary so long as saidlampfunctions correctly, said control comprising a direct coupledtransistor voltage amplifier including an output switching stage havinga base bias circuit wherein the emitter-collector path of said stage isin series with said solenoid and said source, a voltage divider circuitcomprising a two-terminal fixed resistance element connected in serieswith the positioned lamp in said lamp energizing circuit, the ratio ofsaid fixed resistance to the resistance of a heated lamp filament lyingin the range from about 0.01 to about 0.08, and means connecting theterminals of said fixed resistance element to apply the potentialdifierence therebetween as input to said amplifier, whereby to bias saidbase for flow of current in said path to energize said solenoid whensaid potential difference is less than a given value and to hold saidsolenoid de-energized when said difierence exceeds said value.

References Cited in the file of this patent UNITED STATES PATENTS

